QI understand that Social Security benefits are taxable, but how do I calculate what portion of my Social Security benefit is taxed?

AIf your only income is from Social Security, your benefits likely aren't taxable. But if you have other taxable income—such as from a job, freelancing, a pension or withdrawals from tax-deferred retirement savings—then 50% or 85% of your Social Security benefits may be subject to federal income taxes (and Social Security benefits may be taxable in 13 states, too).

To determine the percentage, calculate your "provisional income," which is your adjusted gross income (not counting Social Security benefits), plus any nontaxable interest and half of your Social Security benefits. If that total is less than $25,000 if you're single or $32,000 if married filing jointly, your Social Security benefits are not taxable. If it's between $25,000 and $34,000 on a single return or $32,000 to $44,000 on a joint return, then up to 50% of your Social Security benefits may be taxable. If your provisional income is more than $34,000 on a single return or $44,000 on a joint return, 85% of your benefits may be taxable.

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This calculation, though, only applies to federal income taxes. Additionally, 13 states tax Social Security benefits. Some states, such as Vermont and North Dakota, tax Social Security benefits to the same extent as federal income taxes. But others use different calculations that often have higher income thresholds than the federal rules. In Kansas, for example, Social Security benefits are exempt from income tax for residents with a federal adjusted gross income of $75,000 or less. In Missouri, Social Security benefits are not taxed for single taxpayers with an adjusted gross income of less than $85,000 or married couples with an AGI of less than $100,000. And some income above that level may qualify for a partial exemption in Missouri.